The invention concerns a stabilizer bar in composite construction of fiber reinforced polymer as well as a method for its manufacture.
Stabilizer bars serve in vehicle engineering for coupling the deflection movement of opposed wheels, in particular when maneuvering curves, in order to thus prevent rolling movements. They form a connection between the opposed wheel suspensions of an axle whose middle section is mounted rotatably on the car body or the underbody of the vehicle. The wheel suspensions are connected, mostly by means of elastic elements, to lever-like end members that extend angularly from this middle section.
When, for example, at the time of maneuvering a curve or due to uneven road conditions, only one of the wheels of an axle deflects, the stabilizer bar twists such that also the other wheel is lifted. When the wheel that is loaded more strongly is restored after passing the curve or unevenness, the opposite wheel is lowered also. The force transmission necessary for this occurs through torsion of the middle section of the stabilizer bar as well as through bending and twisting of the angled end members. In addition, the stabilizer bar has a damping function in order to prevent escalating rocking of the vehicle in case of one-sided deflection.
When these stabilizer bars are used, in addition, for the wheel guiding and axle guiding, they are also referred to as guiding stabilizer bars or stabilizer links.
Because extreme mechanical loads can act on a stabilizer bar, primarily pure metal constructions have been used up to now. When manufacturing these stabilizer bars that are mostly made from a single piece of spring steel, first steel rods or pipes are cold-formed or hot-formed to the desired target geometry. In additional working steps, load introducing means, for example, for attaching the stabilizer bar to the underbody, as well as the connecting means for the wheel suspension are joined to the stabilizer bar blank or formed from it. Also known is the manufacture of stabilizer bars in assembled construction wherein middle section and end members are separately produced and joined by material fusing, frictional, or positive fit connections.
Stabilizer bars of metal are very heavy, on the one hand, and, particularly when configured in tubular shape, are susceptible to breakage. Hence, stabilizer bar constructions of fiber reinforced polymer have already been suggested in the past.
DB 3 612 777 A1 describes a suspension for automobiles, comprising a stabilizer bar which is comprised at least partially of fiber composite material. The angled ends of the stabilizer bar are formed from metal and are introduced into it, like the bearing eyes for attachment of force introduction elements, already during wrapping of the form of the stabilizer bar. The stabilizer bar is produced in that additional fabric tubes are applied or fibers are wrapped onto a formed hardened fiber composite fabric tube. This manufacturing process is disadvantageously very complex because the actual fiber construction occurs after forming of the stabilizer bar and therefore the application of more complicated fiber application technologies, for example, braiding or wrapping with which more stable fiber composite structures can be produced, is not possible. Hence, the stabilizer bar disadvantageously is comprised of a plurality of joined fabric tubes or is wrapped discontinuously; this leads to disadvantageous discontinuities in the fiber orientation counteracting optimal force introduction and force distribution.
JP 57022017 describes a method for manufacturing a plurality of stabilizer bars from fiber reinforced polymer in one working step. For this purpose, a fiber material impregnated with polymer is wrapped around a base body and this base body corresponds to the shape of the target stabilizer bar. In this context, on account of the curved geometry of the base body as well as the wrapping of the fibers, thinning and unfavorable fiber orientations, in particular at bending locations, are observed. Subsequently, a mold is placed around this base body and heated. At the same time, the tube located in the mold is pressurized and pressed into the heated mold. Due to the heat, the polymer and the fibers form a firm composite and fix the stabilizer bars in the desired shape which can be separated after hardening and cooling of the matrix material. Because the resulting composite body is separated in the end into several stabilizer bars, the attachment of load introduction or connecting elements can be done disadvantageously only afterwards.
The object of the invention is to overcome the disadvantages of the prior art and to propose a stabilizer bar of fiber composite material in a monolithic construction without fiber interruption for use in land vehicles and rail vehicles. This stabilizer bar should have a stiffness and strength as high as possible with a weight as low as possible as well as load-adapted and improved damping properties. In addition, a method is to be proposed for easy and inexpensive manufacture of such a stabilizer bar.